The impact that certain chemicals used in the manufacture of refrigerators and air conditioners, which have been associated with ozone depletion and global warming, has significantly decreased in the last 15 years, a leading atmospheric scientist said on the heels of a new U.N. environmental report.

Susan Solomon of the National Oceanic and Atmospheric Administration (NOAA) in Boulder, Colo., and co-author of the intergovernmental report prepared for the World Meteorological Organization (WMO) and the U.N. Environment Program (UNEP), said this is a major accomplishment, and the hope is now to provide updated scientific information to governments so they can further reduce these chemicals, known collectively as halocarbons, from the atmosphere.

The new report states that efforts stemming from 1987's Montreal Protocol on Substances that Deplete the Ozone Layer have paid off. The Montreal Protocol called on manufacturers to stop using chlorofluorocarbons (CFCs), the specific halocarbon previously used as the working fluid in air conditioners and refrigerators and most known to damage the ozone layer as well as contribute to the greenhouse effect.

Instead, it was decided by governments that halocarbons such as hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs) be considered, and the choices made among them have had a generally positive effect on the earth's climate. Unlike CFCs, which are considered ozone-depleting substances, HFCs and PFCs don't affect the ozone. They were consequently considered more ozone-friendly and appropriate alternatives to CFCs.

According to Solomon, as recently as 1990, halocarbons, including CFCs, HFCs and PFCs, collectively contributed 33% on top of the worldwide greenhouse effect already caused by carbon dioxide emissions from fossil fuel burning gases. Methane is also known as a greenhouse gas that works to trap radiation and heat in the earth's atmosphere, which eventually causes global temperatures to rise.

But by 2000, the halocarbons emissions were contributing 10% to the overall greenhouse effect, which is a more than 20% decrease in a decade.

Nonetheless, the report did emphasize that HFCs and PFCs currently in the atmosphere are themselves contributing to the greenhouse effect. The concentration of HFCs is also expected to increase in the future. And in an effort to begin to reverse global warming, it recommends that manufacturers and officials of industrialized countries now look to other alternatives outside the realm of halocarbons.

UNEP Director Klaus Toepfer said, "there can be no trade-offs between saving the ozone layer and minimizing climate change."

And Solomon stressed that the issue now is not whether the cure is worse that the disease. "We're really looking at the fact that ozone-depleting substances like the CFCs have been phased out," she said.

She said the intent now is to provide options to governments on how to improve on this progress and, in addition to seeking alternatives to halocarbons in general, further reduce CFC emissions.

Because though the developed world has long halted CFC use, older appliances are still leaking the chemicals into the atmosphere. "It could be something as simple as using better hoses or clamps [to contain leaks]," she said. "What we tried to do was identify options, ranging from simple and cheap to complicated and expensive, and think about which ones, if any, may be useful to them."

Other suggestions in the report include more recycling and the destruction of dangerous substances. Additionally, ammonia, while toxic, has no significant greenhouse effect, and it has also been suggested as another alternative to HFCs and CFCs.

"There is definitely a safety issue with ammonia," Solomon said, adding that old refrigerators made in the late 1800s and the early 1900s used ammonia as refrigerants.

Ironically, the questionable safety of using ammonia and other toxic gases such as methyl chloride and sulfur dioxide as refrigerants was a significant reason that CFCs became the safer refrigerant in the late 1920s, when they were first synthesized, according to NOAA's Climate Monitoring and Diagnostics Laboratory.

While CFCs are safe in the lower atmosphere, they undergo a significant reaction in the upper stratosphere by releasing inorganic chlorine that then destroys the ozone, which normally protects us by absorbing harmful ultraviolet radiation.

The UNEP believes that if these recommendations are followed with safety in mind, however, it could halve the effect of CFCs, HFCs, and PFCs by 2015.

"When the CFCs were phased out, there was a preference for these new replacements," said Bert Metz, a climate change expert who also contributed to the report. "It was thought these were an ideal solution."

Governments should start thinking about how to replace these chemicals, he said, adding that a possible amendment to the Montreal Protocol setting reduction targets for these chemicals could serve as a starting point.

"There is a gap in the protocol," Solomon said.

The protocol has not yet addressed how to handle the older appliances such as refrigerators, air conditioning units and foams in buildings that are continuing to leak gases into the atmosphere.

"The report questions whether or not simple measures of better recovery or destruction would be worthwhile," she said.

As an example, Solomon said that when an old refrigerator is recovered, CFCs should be sucked out of the compressor carefully to make sure nothing leaks, especially if it's to be sent to the junkyard to be destroyed.

While it will take decades to purge the atmosphere, experts said that last September's ozone hole had not increased in size and was about the same as the year before.

The report says, "While considerable variability in ozone is expected from year to year, including in polar regions where depletion is largest, the ozone layer is expected to begin to recover in coming decades — assuming full compliance with the Montreal Protocol."

"Ozone depletion has stabilized now," Solomon said. "It's a success story for the environment."

Nonetheless, despite the phasing out of the use of a variety of harmful gases, the gases that were already emitted will live in the atmosphere for many decades, she said.

"They will take a long time to go away," Solomon said. "The lifespan of the gases is out of our control and it is determined by how rapidly sunlight can break them up. It just happens very slowly."

Average global temperatures rose about one degree in the 20th century, and scientists say that has contributed to the thawing of the permafrost, rising ocean levels and extreme weather. Experts say further increases could seriously disrupt ecosystems, agriculture and human lifestyles.